organism under different nutritional environments. This adaptation requires major changes in the hepatic metabolic gene program. One gene family, long-chain acyl-CoA synthetase (ACSL), encodes enzymes that play key roles in lipid metabolism in liver, as well as other metabolic tissues ( 1-5 ). ACSL catalyzes the formation of fatty acyl-CoA from ATP, CoA, and long-chain fatty acids (FAs). This reaction is the fi rst step in FA metabolism following transport of nonesterifi ed FA into mammalian cells. This activation process is essential for cellular utilization of FA via different metabolic pathways, including the cellular  -oxidation system responsible for FA oxidation (catabolism) and the anabolic pathways for the synthesis of phospholipids, cholesterol esters, and triglycerides (TG). To date, fi ve isoforms of ACSL (ACSL1, ACSL3, ACSL4, ACSL5, and ACSL6) have been characterized in humans, mice, and rats ( 3 ). These isoforms differ considerably in their characteristics, including substrate specifi city, enzyme kinetics, and tissue and subcellular distribution. These individual characteristics contribute to their different cellular functions and metabolic outcomes (6)(7)(8)(9)(10)(11)(12)(13)(14). Because each isoform of the ACSL family has a distinct function in directing acyl-CoA to one or more specifi c downstream pathways, the level of expression/activity of individual ACSL isozymes could directly infl uence FA metabolic fates in liver tissue.Nutritional status and hormone levels differently affect the gene expression of ACSL family members in liver tissue ( 15-17 ). In mice fed a normal chow diet, fasting increased the mRNA abundance of ACSL4 and ACSL1 in the liver, and fasting decreased ACSL3 and ACSL5 mRNA levels. In liver of Wister rat, fasting had little effect on ACSL5 mRNA expression, but refeeding markedly increased Abstract Long-chain acyl-CoA synthetases (ACSL) play key roles in fatty acid metabolism in liver and other metabolic tissues in an isozyme-specifi c manner. In this study, we examined the effects of a fructose-enriched diet on expressions of ACSL isoforms in the liver of hamsters. We showed that the fructose diet markedly reduced the mRNA and protein expressions of ACSL3 in hamster liver without signifi cant effects on other ACSLs. The decrease in ACSL3 abundance was accompanied by a reduction in ACSL-catalyzed synthesis of arachidonyl-CoA and oleoyl-CoA in liver homogenates of hamsters fed the fructose diet as opposed to normal diet. We further showed that fructose diet specifically reduced expressions of three key components of the LXR signaling pathway, namely, liver X receptor (LXR) ␣ , LXR  , and retinoid X receptor (RXR)  . Exogenous expression and activation of LXR ␣ /  increased hamster ACSL3 promoter activities in a LXR-responsive element (LXRE)-dependent fashion. Finally, we showed that treating hamsters with LXR agonist GW3965 increased hepatic ACSL3 expression without affecting other ACSL isoforms. Furthermore, the ligand-induced increases of ACSL3 expression were accompan...